I examined the foraging behavior of the green darner dragonfly nymph, Anax junius, to assess the suitability of odonate foraging behavior as a sensitive endpoint for monitoring contaminant exposure. Odonates are potentially excellent organisms for work in biomonitoring programs because: (1) they have complex foraging strategies that tightly couple sensory cues and mechanical responses: (2) their ecology is well-studied: and (3) they are often the dominant invertebrate predator in fishless systems. Thus they have the potential to structure communities through predation;I tested (1) the possibility that nymphs may regulate populations through frequency-dependent foraging and (2) the relationship between head capsule cholinesterase (ChE) levels in nymphs exposed to an organophosphorus insecticide and subsequent foraging behavior. Functional response models were developed for nymphs fed exclusively midges or amphipods and for nymphs fed mixed prey. Nymphs fed only midges exhibited a sigmoidal type III response (a prerequisite for frequency-dependent foraging); nymphs fed only amphipods exhibited a hyperbolic type II response. These results were reversed in mixed prey trials. Regardless of densities of prey offered, a higher percentage of midges were eaten compared to amphipods. Dragonflies did follow a simplified optimal foraging model based on energy maximization but they did not consistently exhibit frequency-dependent selection;ChE levels were slightly elevated in treated nymphs and foraging behaviors between treated and control groups were not statistically significant, most likely because of high variability in ChE activities within the control group and across treated groups. My results suggest that certain animals may be unsuitable for routine pesticide monitoring and prior to incorporating any species into a biomonitoring program, careful consideration of the species' sensitivity to the contaminant needs to be considered. Further work is needed to determine other factors that may influence ChE levels in species as well.